In recent mobile communication systems, the realization of multimedia wireless terminals capable of transmitting not only voice alone or data alone but also moving pictures has been anticipated. For this purpose, it is necessary to simultaneously transmit signals having diverse communication characteristics, for example, communication characteristics such as those of voices, in which slightly higher error rates are allowable, but large unevenness in transmission lag time are not. A contrasting example is communication characteristics such as those of typical data, in which unevenness in transmission lag time is not a problem, but the occurrence of communication errors is not permitted. In this regard, conventional arts provide methods, such as those wherein channel control information is communicated at high-quality, or wherein transmission quality is differentiated based on data type.
For example, FIG. 26 is a block diagram of a conventional mobile communication system disclosed in Japanese Laid-Open Patent Publication 1998-257097. Japanese Laid-Open Patent Publication 1998-257097 relates to broadband digital wireless systems that transmit data through channels corresponding to the quality required for transmission data by dividing a broadband channel into a plurality of narrowband channels and constantly monitoring the error rate of each narrowband channel. In FIG. 26, at 2101 is a transmission terminal; at 2102, a reception terminal; at 2201a, a transmission wireless module inside the transmission terminal 2101; at 2201b, a reception wireless module inside the reception terminal 2102; at 2202a, a transmission interface; at 2202b, a reception interface; at 2203a, a transmission modulator; at 2203b, a reception demodulator; at 2204a, a transmission controller; at 2205a, a transmission demodulator; at 2205b, a reception modulator; at 2206a, a transmission error detecting/collecting unit; at 2206b, a reception error detecting/correcting unit; at 2207, a broadband channel; at 2208 and 2209, narrowband channels that are divisions of the broadband channel 2207; at 2208, control channels; and at 2209-1 through 2209-n, data transmission channels.
For a clearer understanding, FIG. 26 principally illustrates transmission-related functional blocks in the transmission wireless module 2201a and reception-related functional blocks in the reception wireless module 2201b. The operation of the conventional mobile communication system will be now discussed. In the present conventional example, the broadband channel 2207 is divided into the narrowband channels 2208 and 2209. The interface 2202a of the wireless module 2201a temporarily stores data that the transmission terminal 2101 is to send to the reception terminal 2102. The stored data undergo predetermined modulation processing in the modulator 2203a and are then transmitted to the terminal 2102 through the transmission channels 2209-1, 2 and 3 set by the controller 2204a. The quality of transmission channels not used for data transmission is monitored by periodically transmitting test signals therethrough.
Signals received by the wireless module 2201b are demodulated by the demodulator 2203b and are stored in the error detecting/correcting unit 2206b before being outputted to the terminal 2102. Meanwhile, the error rate of each of the transmission channels 2209-1 through 3 and the error rates of the other transmission channels, which are detected by means of the test signals, are transmitted, as part of the control information, from the terminal 2102 to the terminal 2101 through the control channel 2208.
In the wireless module 2201a, the controller 2204a decides transmission conditions and transmission channels by comparing received error rate information (channel quality) regarding transmission channels with communication characteristics necessary for sending data.
As discussed above, optimal communication is carried out by feeding back the quality of each narrowband channel each time data signal is transmitted, and by satisfying communication characteristics required by the data.
In this manner, feed-back loops that periodically monitor the quality of channels are formed by transferring data and test signals and sending back the error rate information of the transferred data. These feed-back loops are referred to as monitoring periods. In the broadband communication system of the conventional example, transmission conditions (such as data rate, error control method, and wireless packet size) are modified depending on changes in the quality of the channels and the required communication characteristics. In order to decode signals correctly, these transmission conditions need to be sent by transmission terminals to reception terminals, and the setting for a demodulating circuit needs to be modified by the reception terminals in response to these transmission conditions.
In the conventional art described above, especially in wireless zones where data are more likely to suffer losses, due to noise and interference, than in cable zones, when a series of packets was transmitted, a plurality of transmission paths that were different in transmission quality were set for control channels and for data transmission channels, and transmission conditions were modified in response to changes in channel quality and required communication characteristics.
Even among the same kinds of data, such as call voices, there are some important portions where, when losses and errors occur, critical distortions arise in the voices reproduced at the reception side, while there are other portions where voice quality is not affected even when losses occur; however, the selection of transmission quality based on the importance of these portions was not feasible because these portions are typically intermingled in a series of data.
Accordingly, when the important portions suffered losses, the improvement in voice quality could not be implemented and efficiency was low even when the unimportant portions were successfully transmitted. The present invention was implemented in order to address the problems discussed above and to perform, through transmission paths that are different in transmission quality, the transmission of packets created by classifying the same kinds of data according to their importance.
For example, in cases where, with a header and a payload within a single packet, high quality is required for the header while low quality is acceptable for the payload, when the total packet is transmitted through a transmission path where the required demands are high because no means for separately transmitting the header and the payload is available, there is a problem in that the transmission is expensive, because transmission paths where the quality demands are high are utilized even for payloads. In contrast, when the total packets are transmitted through a transmission path where the demands required by the payloads are low, the possibility of incorrect routings for control information increases due to losses in the headers. In these cases, even though the routing for the payload is correctly implemented, its data are wasted; therefore, there has been a problem in that as the possibility of losses of each packet increased, wireless resources between mobile terminals and base stations have been wasted. In order to cope with this problem, the present invention divides packet segments within a single packet further into a header and a payload, and transmits the header through a transmission path whose required quality is high, and the payload through a transmission path whose required quality is low.